Travis Road is one of a hundred dirt lanes that road crews in this part of southeastern Michigan haven't gotten around to paving. On this late November day, a cold, steady rain has enlarged the potholes into craters that bounce my car as I approach a large, nondescript metal building. It's the kind of obscure facility that's sprinkled across the older suburbs of Michigan, Ohio, and the rest of the car-building belt of the Midwest. GM's Milford Proving Ground is 10 miles to the north, the border of Detroit 25 miles to the south. A small sign outside says PSI SPRINGS.

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Inside is the guy everyone says I need to talk to, Steve Bown. He is tall, with wide shoulders and noticeably broad hands that make him look more like a tight end than someone who devotes his waking hours to the minute details of valve springs. He drops me off in the conference room and leaves to fetch his partner, Larry Luchi. And then I spot it on a dusty shelf: a heavy, slightly blackened coil mounted on a small piece of wood. A plaque underneath reads "Jeff Gordon, 1998 Rockingham Win." This tube of steel wire was the first PSI valve spring used in a Nascar race. It revolutionized engine building and the country's most popular motorsport, but few people have ever heard of it.

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My interest in the subject began with a remark by legendary Nascar team owner Jack Roush. This was 15 years ago. I casually asked him if there was a single automotive part with the potential to dramatically alter racing stock cars. Roush isn't in the business of disclosing trade secrets, but he lit up. "Oh, yeah," he said enthusiastically. "Valve springs. We're getting higher quality valve springs that are going to let us do some tremendous things." It was an unexpected answer: These springs are humble engine parts. They simply keep the valves to the combustion chambers closed until the moment that a fresh dose of mixed fuel and air has to enter, or exhaust leave. Roush wouldn't elaborate—maybe he thought he had said too much already. Intrigued, I called other Nascar teams. But racers are as tight with their secrets as the NSA. I got a bunch of "no comment" answers and moved on.

Recently, Nascar's big rules change for 2012—a switch from carburetors to electronic fuel injection—made me wonder whether the innovations Roush hinted at had really changed the sport. I dug back into my contacts among Nascar team owners and engine builders. This time I was able to get people to talk. The highly publicized switch to fuel injection was a sideshow, they told me, in comparison with the changes in engine performance that occurred between 1998 and 2004. During those years, horsepower and engine revolutions had reached once-impossible heights. To understand how, I needed to ask Steve Bown about his valve springs.

Bown and Luchi return to the conference room, where I am contemplating the Jeff Gordon spring. "We were in the pits during the race," Luchi says. "Keeping our fingers crossed watching the 24 [Gordon's] car." It wasn't a particularly exciting race. Videos show Gordon hanging back for most of the contest but clearly dominating the final third of the race. At one point he has a 4-second lead. Gordon had just won the 1997 Nascar championship, and fans had no reason to suspect that anything other than driving skill was at work. But Nascar engineers knew. Inside his engine, 16 newly designed valve springs were ticking away, giving him an advantage. "By 2001," Bown says, "all the teams were using our springs."

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Rules governing Nascar engine architecture date back 50 years. They have evolved, but the basic regulations that limit engine size to 358 cubic inches and define the layout—two valves per cylinder and pushrod valvetrains—were written in 1968. For that reason, Mike Fisher, Nascar's managing director of research and development, has a strange job for someone with his title: keeping a lid on innovation. "We try to maintain a pretty tight box around what teams can do to the engine," he says. "We don't want one team having more power." If the details can seem backward, like running carburetors and burning leaded fuel decades after passenger cars had moved on, there's a certain genius to the strategy. Nascar grandstands are packed partly because, in any given race, there are at least a dozen drivers who could win. In terms of lead changes and tight racing, a Formula 1 race is, by comparison, a procession.

Despite the straitjacket rules, however, Nascar drivers, engineers, and mechanics have always hunted for ways—some legal, others not so much—to get a performance edge. Counterintuitively, massaging the old tech of the Nascar V-8 at the granular level has produced highly advanced engineering. When it came to engine design, though, there was always one weak link. "The vast majority of engine failures—85 to 90 percent—are caused by broken valve springs," says Cecil Stevens, a longtime engine builder who now heads the engineering consulting firm Illusions Engine Development. The reason is simple: Valve springs have an incredibly tough job.

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At each of the engine's eight cylinders, the intake valve lets in fresh air and fuel, and the exhaust valve releases spent gases—16 valves in total. A spring holds a valve closed until the valvetrain system pushes on the top of the spring, forcing the valve to open. Since an engine's output is directly related to the amount of air that flows in and out of the combustion chamber, the valves play a vital role. The larger the valves, and the farther they open, the greater the airflow and the horsepower the engine can produce—and the greater the stress on the spring.

As much as airflow dictates engine power, so does the speed at which the engine operates. Spin an engine faster and it will, in most cases, make more power. Randy Dorton, the chief engine builder at Hendrick Motorsports, Gordon's team, started a quest in the early '90s to increase engine rpm. Dorton died in a plane crash in 2004, but Jeff Andrews, who is now Hendrick's director of engine operations, has been at the team for about 20 years.

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"Back then," Andrews says, "the biggest limiting factor [for higher engine rpm] was the valve springs." In 1998, a stock car's V-8 peaked at about 8000 rpm. The valves cycle at half the speed of the engine's crankshaft, so at 8000 rpm the valves open 4000 times per minute, or 67 times each second. During many oval races, engines remain at peak rpm for 500 miles—and the valve springs were operating outside their comfort zone.

The springs were a commodity product. Teams bought them from companies whose steady clients were mainstream carmakers. One such company is Peterson Spring, a privately held automotive supplier founded in Detroit in 1914. Dorton approached Peterson about building better valve springs. The company made some improvements, but it simply wasn't focused on racing. While there, Dorton met Peterson engineer Steve Bown and ultimately convinced him that there was a need for a company that focused on racing valve springs. Bown enlisted Larry Luchi, a former Peterson CFO, to handle the business details while he focused on design and manufacturing. In 1996, with $170,000 of startup capital, the two men formed Performance Springs Inc. (PSI). "During our first year, we had one customer," Luchi says. "Hendrick Motorsports."

Jeff Gordon on his way to winning the 1998 GM Goodwrench Service Plus 400 at North Carolina's Rockingham Speedway. Few knew about the advanced valve springs inside his engine.

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Tractor-tire-size spools of steel wire squat in the rear of PSI's minifactory. Bown guides me to a coiling machine that's about the size of a large refrigerator. Hydraulics draw the wire, and dies guide it into the spiral shape. When the spiral reaches a size dictated by computer controls, a cutter clips the wire and the newly born spring joins countless others in a bin. This first step in the process differs little from what you'd see in any spring factory. What comes next is the unique part: PSI's 41 employees take the springs through a nearly 50-step treatment process, coddling the parts like diamond-cutters tending gems. "We focus on quality, not cost," Bown says.

One of PSI's main goals now is to increase the fatigue resistance by reducing the number and size of microscopic flaws in the metal.

When steel wire is coiled into a spring, the metal becomes rough, like a board cut on a table saw, although the flaws are all but invisible to the naked eye. PSI heats its springs to more than 1000 degrees Fahrenheit in an oven that looks like a giant toaster, quenches them back to room temperature, shot-peens them in three steps—the process is similar to sandblasting, but the medium is much finer—and polishes them. That's the quick version. It took Bown an hour to walk me through the process, and he declined to divulge many of the details. The finished product is actually two concentric springs, a design that increases spring rate—the force required to compress it a given distance—while ensuring that the piece can still fit in the allotted space. As a final step, workers in a darkened room inspect each spring under a microscope. If they find a blemish, it gets pitched. The rejection rate is about 25 percent.

Engine builders have their own way of testing springs: They use a Spintron, a machine invented in 1993 by Bob Fox to test the pushrods made by his company, Trend Performance. It's a simple device, basically an engine block with only a dummy crankshaft and the valvetrain components—camshaft, pushrods, rocker arms, valves, and springs. The engine doesn't run; it's cycled by a 60-hp electric motor connected to the crankshaft. With an array of sensors and high-speed video cameras, the Spintron reveals formerly invisible details, like how an undamped spring continues to oscillate after the valve closes.

In the win-at-all-cost culture of Nascar racing, where budgets hover at around $20 million and winning the championship is a financial windfall, teams lined up to buy $60,000 Spintrons, which validated parts and became invaluable research tools. And few balked at the extra expense of the PSI springs—$28 apiece, or 40 percent more than previous springs. But while the springs themselves weren't pricey, they unlocked a technological arms race that did prove expensive.

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Once valve springs were no longer the limiting factor on engine rpm, other weaknesses emerged. Doug Yates is the president of Roush Yates Racing Engines, a company that builds more than 500 Nascar engines a year. "Once you got a better valve spring," he says, "you could spin the engine faster. But for every extra 100 rpm, the next weakest link showed up." Piston assemblies were lightened to lower the forces caused by the higher speeds. The camshaft was positioned higher in the block to reduce the length and the weight of the pushrods. Special coatings and bearings reduced friction.

In 1998, the best Nascar V-8s revved to about 8200 rpm and produced roughly 700 hp. In the following six years, the maximum engine rpm climbed to 10,500 and the horsepower to 900. In the process, the Nascar engine builders broke through what were once thought to be ironclad boundaries. Take piston speed, for example. It was once believed that the upper limit for the piston speed of a Nascar V-8 was about 4500 feet per minute (fpm). F1 engines, which are considered to be the most sophisticated racing engines, have piston speeds of about 5200 fpm. But in 2004, the Nascar V-8 outdid even the F1 motors with piston speeds of 5400 fpm. "The F1 guys came over," Yates says, "and they couldn't believe what we'd done."

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These changes weren't cheap. Say a team designs a new camshaft that opens the valve farther, to take advantage of the new springs. Testing the cam requires a new set of valve springs ($500), the camshaft ($3000), valves ($3000), and assorted other costly items, all adding up to about $10,000. To validate the test, it has to be repeated, so it's $30,000 for just one new part. If something fails, the part gets redesigned and the tests repeated. Now multiply that process over the hundreds of parts in an engine. "It was a financial war to not only get an edge, but to simply keep up," Yates says. The result was to concentrate a significant horsepower advantage at the few shops that could afford to develop the high-revving engines. By the early 2000s, according to Andy Randolph, technical director at Earnhardt-Childress Racing Engines, the field was splitting between those teams that had engineered high-rpm engines and those that hadn't. "The races were turning into rpm battles," he says.

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This rpm race ended in 2005, when Nascar, concerned about maintaining a level playing field and limiting top speed, introduced the gear rule. By mandating specific gear ratios for each track and applying a little math, race officials can compute the maximum engine rpm. "It's the mechanical way to control engine rpm," Nascar's Mike Fisher says. "We target about 9000 to 9200 rpm on a steady basis, with a peak of about 9500."

The effects of that tumultuous six-year period are in plain view every Sunday. Today, engines are relatively unstressed, which is why failures are now rare. And where once more than a dozen shops and teams produced engines, now there are just a handful. For the moment, the field has been equalized: Last year, there were 17 different winners, a 30 percent increase over 2008.

At PSI, they're still testing and tweaking. Before I leave, Bown shows me the latest prototype. I hold it up next to the Jeff Gordon spring. The new one is half as thick. "We're getting steel made specifically for us," Bown says, "and the springs can withstand even higher stress levels." That means the engine builders can open the valves a little more, inching up the power levels again. So far, no team is using the new spring, but it's only a matter of time. There are rumors that some teams have found a way to increase engine rpm past 9500, despite the gear rule. They continue to experiment with aerodynamics, suspensions, and tires. And lap times drop a bit each year.

Pushrod-actuated valves may seem outdated—the layout is as old as the internal combustion engine—but refinements to the design have never stopped coming. GM and Chrysler still build pushrod engines.